This invention relates to a control element arrangement for controlling the steering angle of a motor vehicle and, more particularly, to a control element arrangement for controlling the steering angle of a motor vehicle having a user-operable control element by whose operation a steering angle adjusting unit which is mechanically uncoupled from the control element can be controlled for the steering angle adjustment of vehicle wheels.
In the case of a conventional steering wheel arrangement for the steering angle control, the steering angle adjustment takes place by the direct mechanical transmission of the rotating movement of the steering wheel to the respective vehicle wheels. It is known to provide, instead of a steering wheel, a user-operable control element which is mechanically uncoupled from the steering movement of the wheels. By means of the operation of the control element, a steering angle adjusting unit can be controlled instead which, in turn, carries out the corresponding steering angle adjustment of the wheels. Such an arrangement with a manually operable control element is described in the article by H. Bubb, "Work Site--- Driver, An Ergonomic Study", Automobil-Industrie 3/85, Page 265. Other similar arrangements are described in U.S. Pat. No. 3,022,850 and in the Convention Volume Publication by Branneby, et al., "Improved Active and Passive Safety by Using Active Lateral Dynamic Control and an Unconventional Steering Unit, 13th International Technical Conference on Experimental Safety Vehicles, Proceedings Vol. 1 , Nov. 4 to 7, 1991, the disclosures of which are incorporated by reference herein as non-essential material.
Because of the mechanical uncoupling of the control element from the pertaining steering movement of the wheels, in the case of such arrangements, the reaction force effect of the steering rotating movement of the wheels on the control elements which is customary in conventional steering wheel arrangements is naturally absent. As a replacement, it is suggested in the above-mentioned U.S. Pat. No. 3,022,850 to design the control element in the form of a control stick with a comparatively heavy upper end head whose inertial force is opposed to the operating force exercised on the control stick by the user and, as a result, counteracts increasing steering angles. As a result, the operator is to receive a certain reaction force acknowledgment concerning the intensity of the respective demanded steering angle, and by means of this measure, the steering is to be slightly stabilized when there is a danger of swerving.
In the above-mentioned Convention Volume Publication, P. Branneby, et al. suggest that the control element arrangement be designed such that a reaction force is exercised on the control element which is to be overcome for operating the control element. As the size of the steering angle increases, the reaction force rises preferably non-linearly, for example, in sections linearly with a hysteresis, in which case the sensitivity of the steering angle adjustment is simultaneously increasingly selected as a function of the vehicle speed with a higher longitudinal vehicle speed.
The present invention is based on the technical problem of providing a control element arrangement of the above-mentioned type in which case the user receives a reaction force acknowledgment, which is as informative as possible, on the control element for the intuitive detection of the steering-angle-related driving situation.
This problem is solved by a control element arrangement according to the present invention having a user-operable control element by whose operation a steering angle adjusting unit which is mechanically uncoupled from the control element can be controlled for the steering angle adjustment of vehicle wheels. A reaction force mechanism is provided which exercises a reaction force on the control element which counteracts the control element operating force and which rises with an increasing steering angle size (.alpha.) as well as with an increasing longitudinal and/or lateral movement of the vehicle.
This arrangement according to the invention contains a reaction force mechanism whose construction can be of a conventional type for exercising an active reaction force on the control element, in which case it is now designed such that the reaction force which is exercised on the control element and counteracts the operating force of the control element rises not only as the size of the steering angle increases but also with an increasing longitudinal and/or lateral movement of the vehicle. In this case, the reaction force may be limited in the upward direction by a maximum force. Analogously, as required, the control element deflection may be limited by an appropriately high reaction force. The linking of the reaction force component which depends on the size of the steering angle with the reaction force component which depends on the longitudinal and/or lateral movement of the vehicle can take place in different fashions, for example, by adding or multiplying. The reaction force, which is actively exercised on the control element mechanically uncoupled from the steering movement of the wheels simulates in a fashion which is close to reality the steering stiffness customary in conventional steering wheel arrangements.
In a further advantageous development of the invention, the reaction force component which is dependent on the longitudinal speed of the vehicle will linearly increase with a rising speed only when a certain minimum speed is exceeded.
In a yet further advantageous development of the invention, the reaction force component which is a function of the size of the steering angle is varied as a function of the vehicle speed by the fact that the value of this reaction force component at the break, which connects two linear sections of the characteristic curve of a different slope with one another, is selected to fall with an increasing longitudinal speed, whereby the rate of change of this reaction force component becomes smaller with a rising longitudinal speed of the vehicle in the range of small steering angle sizes and increases in the range of large steering angle sizes. As required, the characteristic curve of the reaction force component may contain several such breaks and thus may be composed of more than two linear sections having different slopes.
A further advantageous development of the invention provides the user with an intuitive acknowledgment which can be detected by way of the control element and which indicates that the vehicle has reached a driving-dynamic limit situation. In this case, the reaction force applied to the control element contains a vibration force component, in which case for a further intuitive information concerning vehicle dynamics with a driving situation which becomes more critical, its vibration frequency will fall and/or its vibration amplitude will rise.
When the control element is arranged laterally next to a vehicle operating site, and when it can be manually operated in the transverse direction, it is advantageous in a further development of the invention to design the reaction force applied to the control element asymmetrically. Specifically, at the same longitudinal speed of the vehicle and the same steering angle size, the reaction force is designed to be higher in the direction of the vehicle operating site than in the opposite direction (away from the operator). This corresponds to the fact that the user situated at the vehicle operating site carries out an operation of the control element in the direction away from the vehicle operating site essentially only by the pressing of the thumb, whereas, for operating the control element toward the vehicle operating site, he can use all four other fingers of the hand reaching around the control element.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.